Since no browsers can access the txu.com site, have a look at your HOSTS file.
HOSTS, (no file extension), is located in the "C:\WINDOWS\SYSTEM32\DRIVERS\ETC" folder and is a file that browsers always check before searching the internet for a url web address. If it finds no related entry in that file, it will then continue on sending a search request through the internet. If it does find an entry, it will redirect to wherever the HOSTS says, usually 127.0.0.1 which is back to your computer.
Open HOSTS by right clicking and selecting Open, then select Notepad. Be sure you do not select the "Always use this application for this type of file" option.
If you find an entry see where it is being redirected to, and delete the entry if need be. If you make any changes and re-save the file, be sure to save it as an All file types, and not as a .txt file.
See if that is the cause. If not, perhaps others here will have better ideas.
I have a brand new machine Intel QUAD Q6600 2.4Ghz, 3gb ram. Windows XP Pro. No matter what I do this machine will not access txu.com. I have 3 PCs, I laptop, PS3, Wii, PSP all going through the same Linksys router, and AT&T DSL modem and my new machine is the only one that cannot resolve txu.com. From day one it's never accessed the site. I have IE7, Firefox, Safari and none of them can reach txu.com. I've run RegCure and other registry cleaners to no avail. None of my IT colleagues have ever seen this problem before. Every now and then I see a DNS frame error of some kind flash on the lower left screen. I've also run all ipconfig dns commands.